This project deals with the problem of restoring lower limb function to patients who require the use of a knee/ankle/foot orthosis (KAFO) for ambulation and must have the knee locked for stability during gait. These patients typically have neuromuscular conditions which weaken or paralyze the hip extensors and/or the ankle plantar flexors, in addition to weakened or paralyzed knee extensors. Currently these types of patients are usually fitted with either a conventional long leg brace which has a knee joint equipped with a mechanical manual lock or a free knee brace equipped with an eccentric knee joint. These bracing schemes result in lack of movement of the knee during the swing phase of gait, which results in an inefficient gait. The goal of this project is to design, develop and test a small, lightweight, electronically controlled knee joint that can be installed on a conventional long leg brace. The knee joint will unlock during the swing phase of gait and lock during the stance phase of gait. To accomplish this goal, we propose to: 1) incorporate modular electronics which sense limb loading to activate a wrap spring clutch control mechanism at the knee, 2) evaluate the gait efficiency of patients using the proposed orthosis through movement analysis, mechanical energy consumption, and physiological costs of ambulation, and 3) determine the best criteria for patient selection based on the experimental trials of this device. The results of these studies are expected to improve the efficiency of gait in patients requiring conventional long leg braces. This type of brace will be useful for patients with poliomyelitis, spinal cord injuries, myopathic disorders, congenital spinal defects, and acquired paralysis due to infections or vascular insults.